Because of the known deleterious effects of the commonly used anionic detergents on the skin, research and development efforts continue unceasingly in an attempt to formulate milder liquid detergent compositions, i.e., liquid compositions exhibiting reduced skin-irritation effects.
Generally, research efforts have fallen in three categories. The first category embraces the efforts to formulate milder liquid detergent compositions by utilizing specific mixtures of particular surfactants in specific proportions. For example, U.S. Pat. No. 3,223,647 discloses mixtures of C.sub.9 --C.sub.15 alkylbenzene sulfonate and tertiary amine oxide in 20:1 to 1:5 proportions which exhibit reduced skin irritation effects. Further, U.S. Pat. No. 3,793,233 discloses mild liquid compositions containing specific proportions of an alkyl ether sulfate containing 5-12 ethylene oxide groups in the molecule, a lauryl sulfate detergent, an alkyl glyceryl ether sulfonate detergent and a trialkyl amine oxide. Similarly, U.S. Pat. No. 3,943,234 discloses a mild liquid surfactant containing trialkyl amine oxide in combination with an anionic sulfate detergent. The foregoing compositions are described as mild because the trialkyl amine oxide reduces the skin irritating effects of the lauryl sulfate and C.sub.9 --C.sub.15 alkyl benzene sulfonate detergents. However, such compositions are not completely satisfactory and the essential amine oxide surfactants may form nitrosamines which may be carcinogens.
The second category of research embraces the attempts to reduce the skin irritating effects of water-soluble anionic detergents containing sulfate, sulfonate and carboxylate solubilizing groups by addition of a specific compound. For example, U.S. Pat. No. 3,548,056 describes the addition of a protein hydrolysate having a gel strength of 0 Bloom grams to dishwashing liquids containing C.sub.9 --C.sub.15 alkylbenzene sulfonate to reduce skin irritation. Similarly, U.S. Pat. No. 4,087,518, British Pat. No. 1,122,076 and U.S. Pat. No. 4,115,548 describe the use of other protein hydrolysates or derivatives thereof to reduce the skin irritation effects of anionic sulfonate and sulfate detergents. Additionally, U.S. Pat. No. 3,944,663 discloses addition of polyethylene oxide to liquid detergents containing a mixture of C.sub.9 --C.sub.15 alkylbenzene sulfonate and C.sub.12 --C.sub.15 alkyl ether triethylenoxy sulfate to reduce the skin irritation characteristics of the liquids. However, these approaches have achieved limited success and tend to be expensive because of the high cost of the added component.
The third category of research concerns the substitution of alternative surfactants, e.g., ampholytic surfactants, nonionic surfactants, etc., for the high foaming anionic sulfate, sulfonate and carboxylate detergents. However, this approach, too, has not been successful because the ultimate products either are too costly or exhibit reduced foaming characteristics.
The present invention represents another improvement in the first category because it relates to liquid compositions which exhibit enhanced mildness, i.e., reduced skin irritation effects, without reduced foam volume and/or foam stability and/or grease emulsification properties and are based upon use of controlled proportions of specific surfactants.